Study Of The Photoinduced Dynamics Of Tetraphenylporphine And Its Derivative

Porphyrins and Metalloporphyrin rings are found in a variety of important biological systems such as hemoglobin,chlorophyll,server as active components of the system with functions ranging from oxygen transfer and storage to electron transfer, as such, are at the focus of a wide variety of research efforts, especially in the research of Porphyrin Biomimetic Chemistry, which aims to synthesize porphyrins to mimic the mechanism of electron and charge transfer kinetics of photosynthesis.Research on relaxation dynamics of excited state of porphyrins contributes greatly to an understanding of the basic mechanism of photosynthesis. With the development and improvement of the theory and technique, scientists can explore the biological photosynthesis further than before, but the short-time dynamics during 0 to 50 fs in Franck-Condon region of the molecular excited state can not be still detected even by the most advanced femto-second ulfast time-resolved laser technique. Resonance Raman spectral techniques, based on Quantum wave packet theory , have a unique advantage on the research of short-time dynamics.In this paper, meso-Tetraphenylporphine,meso-Tetra(p-aminophenyl)porphine,meso-Tetra(p-hydroxyphenyl)porphine,Zn(II) meso-Tetraphenylporphine have been synthesized and the short-time dynamics of photo-induced Charge-Transfer of them have been investigated by the Resonance Raman spectra in combination with DFT calculation. Main contributions of the present work are summarized as follows,(1) The absorption spectrum of Tetraphenylporphine (TPP) in dichloromethane solution was acquired and explained on the basis of Gouterman's four orbital model and electronic orbital calculations。The experimental 400 nm,418 nm,513 nm,551 nm absorption band are,respectively,assigned as B₂,B₁,Q_x,Q_y.Measurements of depolarization ratios of scattering can give information about the symmetry of electronic states. Resonance Raman spectra were acquired for TPP in dichloromethane solvent with 397.9 nm,416 nm,435.7 nm and 514 nm excitation wavelengths. The resonance Raman spectra indicate that the short-time photo dynamics of TPP have significant multidimensional character distributed over a wide variety of vibrational modes such C_m-ph stretch (ν₂₁,1237 cm^-1),phenyl C=C stretch (ν₉,1602 cm^-1),the Porphin ring C_β=C_βstretch (ν₁₁,1553 cm^-1,ν₁₃,1500 cm^-1),the Porphin ring C_m=C_αstretch (ν₇₁,1457 cm^-1,ν₁₅,1440 cm^-1),Porphin ring breath (ν₂₈,1006 cm^-1,ν₃₁,967cm^-1), pyrrole deformation modes (ν₃₄,886 cm^-1,ν₃₆,837 cm^-1),pyrrole half-ring stretching modes(ν₁₇,1363 cm^-1,ν₁₉,1295cm^-1) and pyrrole quarter-ring stretching modes (ν₇₃,1373 cm^-1,ν₇₄,1330 cm^-1), while the vibrational modes in wavenumber and in description for different resonance Raman spectra are very similar, the intensity patterns are very different, it can be explained that the major short-time photo dynamics in the Franck-Condon region of the B band occurs mostly along the nominal C_m-ph stretch and the nominal Porphin ring C_β=C_βstretch ,while for the photo dynamics of the Q_x band occurs mainly along the nominal Porphin ring C_β=C_βand the nominal C_m-ph stretch .The appearance of A₂ non-total symmetry vibrational modeν₇₁ [ν(C_mC_α)as stretch]andν₇₃,ν₇₄ [pyrrole quarter-ring stretching modes] indicate that while most of the excited state structural dynamics are along the total symmetry vibrational reaction coordinates, it also moves along the non-total symmetry reaction coordinate significantly, which means the existence of the Franck-Condon region vibronic coupling between the By,Bx and Q_y electronic states.Reference to experimental results and literature,we have deduced the relaxation dynamics of porphyrin. In our model of relaxation process, the two higher singlet states undergo internal conversion to Q_x within 100 fs.(2) We have also synthesized meso-Tetra(p-aminophenyl)porphine (TAPP),meso-Tetra(p-hydroxyphenyl)porphine(THPP) and obtained their resonance Raman spectra in order to investigate the effect of substituent on the short-time photo dynamics. The resonance Raman spectra indicate that the short-time photo dynamics of TAPP and THPP also have significant multidimensional character with the reaction coordinates or displacements occurring with C_m-ph stretch,phenyl C=C stretch),the Porphin ring C_β=C_βstretch,the Porphin ring C_m=C_αstretch,Porphin ring breath,pyrrole deformation modes,pyrrole half-ring stretching modes and pyrrole quarter-ring stretching modes.The existence of A₂ non-total symmetry vibrational modes which denote the Porphin ring C_m=C_αasymmetric stretch and pyrrole quarter-ring stretch indicate the happeness of Franck-Condon region vibronic coupling between the different electronic states.The introduction of substituents does not affect the relaxing process of porphyrin but cause the red-shift of electronic absorption spectra,because substituents of amino, hydroxyl increase charge density of the porphyrin ring and make transitions between the orbits of energy gap smaller.(3) We have also conducted the study of Zn(II) meso-Tetraphenylporphine. Compared with meso-Tetraphenylporphine, we found that although the main vibration modes in the resonance Raman spectra did not changed, the reaction coordinates or displacements also occured with C_m-ph stretch,phenyl C=C stretch,the Porphin ring C_β=C_βstretch,the Porphin ring C_m=C_αstretch,Porphin ring breath,pyrrole deformation modes and pyrrole half-ring stretching modes, with the introduction of metal ion, the metal porphyrin not only have a higher symmetry, which cause the vanish of A₂ non-total symmetry vibrational modes,but also make the energy gap larger,which result in 1.5 ps of relaxation time.